IT201600079657A1 - DEVICE AND MEASUREMENT SYSTEM - Google Patents

Description

DEVICE AND MEASURING SYSTEM

DESCRIPTION

Technical field of the invention

The present invention refers to a device for the indirect measurement of a physical / chemical parameter of a work environment, calculated on the basis of a remote characterization of the electromagnetic state of a transponder located in that environment, influenced in a known and measurable way by said physical / chemical parameter.

Background

Transponders are transmitter-responder devices (tags) which generally consist of an electronic chip suitable for storing data electrically connected to an antenna. Such devices generally rely on RFID technology. To read or write access to the data stored in the transponder, devices commonly defined as "readers" or readers are used.

Conventional readers are designed to acquire information of a "logical" nature from the tag (ie the content of the non-volatile memory of the chip) but do not provide information on the behavior of the "physical layer", ie on its electromagnetic status.

In particular, there are transponders defined as "active", which have their own power source (eg batteries), and "passive" transponders, which do not have their own power source. This energy source is necessary if you want the transponder electronics to continue to function even when it is not coupled to the reader (for example if it is required that it operate as a data logger). The passive transponders are powered, and therefore activated, by the magnetic field radiated by the respective reader devices. When a passive transponder is outside the coverage area of the electromagnetic field emitted by the reader, it is electrically off, hence the definition "passive".

In commonly used RFID systems, the information exchanged between the reader and the transponder depends on the content of the memory of the chip present on the tag and on the logical operations that the reader requests from it. In some contexts, however, it is required or desirable that the information acquired by the reader depends on one or more environmental parameters detectable by the tag.

In this case, depending on the intended use, it is possible that the transponders integrate sensors for the detection of environmental parameters. The tags with sensors on board must be able to interface with the outside in order to detect the parameters relating to the environment in which they are immersed.

In particular, the detection of the variables connected to the climate (pressure, temperature, humidity), of those connected to the presence of gas or other chemical contaminants and to contact with specific biological agents plays a crucial role in determining the pervasive diffusion of RFID systems both in civil and industrial contexts.

Application cases can be envisaged, among other things, in the monitoring and control of the operation of industrial equipment and / or "hostile" environments, where spaces are narrow and the environmental conditions are unfavorable from a chemical point of view (presence of contaminants, chemical, biological agents) and physical (particular lighting conditions, humidity, etc.).

Furthermore, thanks to the very low costs and ease of implementation, transponders have increasingly integrated into products used in everyday life, including with regard to disposable products and packaging. For example, applications are widespread in the sectors of access control, logistics, in particular for the transport of baggage, passengers, goods and it would be desirable that, through the application of appropriate sensors, applications related to the monitoring of foodstuffs could implement control on the state of conservation of the products, which can be inferred once the environmental parameters have been detected.

The most usual approaches adopted in the realization of sensitive tags provide for the presence on board of the transponder, as well as the sensor for the measurement of environmental parameters, also of a chip or a microcontroller specifically designed for acquisition, processing and storage of the data collected by the sensor. In these cases, the physical quantities of interest are transduced into electrical signals which are then digitized and stored in the transponder chip until a reading operation is performed from the outside.

Generally, in the case of active transponders, the energy to acquire the data from the sensors is provided by a durable energy source. In the case of passive or semi-passive tags, the energy required to operate the tag persists for a very limited time. In particular, passive tags extract the power supply from the carrier of the signal transmitted by a reader device until they are coupled with it.

It is also clear that implementing the possibility of acquiring the sensory data on board the tag involves the use of more sophisticated, expensive and energy-intensive chips than those dedicated to common PICCs (proximity integrated circuit cards).

On the other hand, an opposite approach consists in moving to the reader the intelligence necessary to detect, digitize, process and store the data acquired by the sensor on the tag. The advantages related to this solution are many:

- not having to resort to active tags - eliminating the need for on-board batteries to power the sensor;

- do not increase the cost of tags - as there is no need for chips specifically designed for sensitive tags; And

- manage the complexity of operations on the data acquired on the reader side, where you can count on a greater availability of storage memory and computing resources.

In this second case, the effect of the sensor on the tag-reader system consists in modulating the electrical signal exchanged between the transponder and the reader so as not to affect communication, at least according to the methods provided for by the most commonly adopted standards, but introducing in the signal information relating to the transduced quantity.

The disadvantage of this approach (compared to the adoption of an active tag), however, is that of being able to acquire the magnitude detected by the sensor only when the transponder is coupled with the reader. If the sensor has an "instant" behavior (ie without memory) this implies that only the current state of the work environment can be acquired. If, on the other hand, the sensor has a memory effect, the electromagnetic response acquired by the reader will result from the sequence of past states through which the work environment has evolved.

At the state of the art, as regards the approach with signal analysis to the reader, the presence of numerous applications of RFID systems, generally characterized by high complexity, can be found.

For example, the document US20120182147A1 describes a UHF tag, whose physical behavior variation is obtained by placing a sensitive element on a precise area of the loop or antenna. A very complex reader is further described, which uses ASK and phase demodulation at the same time.

As regards the development of equipment suitable for the characterization of sensors for gases and vapors, in the course of at least the last 20 years systems with considerable construction complexity and dimensions have been developed.

They have considerable costs not only due to the need to be installed in laboratories equipped with complex and expensive utilities (pure gas lines, high pressure cylinders, etc.)

but also because, if, as in our case, the detection method is based on the analysis of the electrical admittance spectrum of the transponder, the electrical part of the apparatus must in turn be a laboratory characterization system since it must be able to accurately detect the presence of resonance peaks and the relative variations in the RF spectrum affected by the transmission. However, this instrumentation is by its nature expensive, bulky and delicate, therefore not suitable for being transported or put into operation in real environments (production line, glove box in a chemical laboratory environment, etc.).

Summary of the invention

The technical problem posed and solved by the present invention is therefore that of providing a device for measuring or rather acquiring the sensory data (for simplicity also referred to as a reader or reader), which can be associated with preferably passive transponders, which allows to overcome the aforementioned drawbacks. with reference to the known art.

This problem is solved by a device according to claim 1.

There is also a system claim 11 and a method claim 19.

Preferred features of the present invention are the subject of the dependent claims.

The invention provides a measurement device for the remote detection of a chemical / physical parameter of a work environment.

The remote detection is achieved by characterizing the state of the RF part of the resonant electrical circuit of a transponder located in the considered work environment, in particular by comparing this state (which is reflected on the impedance spectrum recorded at the reader) with a known electromagnetic reference state.

For this purpose, the transponder is configured in such a way as to present a magnetic / electrical parameter (typically the equivalent electrical capacity of the circuit) which varies according to the chemical / physical parameter to be measured according to a known law with respect to a reference condition.

The measurement device according to the present invention substantially comprises a control and data processing unit, a unit for generating an electrical signal, a unit for receiving an electrical return signal and electromagnetic coupling means with a transponder.

These electromagnetic coupling means with the transponder are made by means of a transmission antenna connected to the electrical signal generation unit, and a reception antenna configured to link the magnetic field reflected by the transponder.

The transmission antenna is configured for the production of a magnetic field in the vicinity of the transponder starting from the electrical signal produced by the generating unit. Said magnetic field, in the case of passive transponders, also powers the transponder itself.

The receiving antenna is connected to the receiving unit in such a way as to provide the latter with an electrical return signal related to the magnetic field reflected by the transponder.

The magnetic field reflected by the transponder, and therefore the electrical return signal associated with it, are influenced by variations in the electrical / magnetic parameter (or electrical / magnetic parameters) of the transponder sensitive to the measurand (s) of interest. The measurand is the chemical / physical parameter to be measured.

The receiving unit is designed to extract from the return electrical signal an electrical signal containing the parameters of interest that is suitable to be acquired and processed by the control unit. The control unit is in turn programmed to process the electrical return signal, store it and present it appropriately to a processing system suitable for calculating the value of the chemical / physical parameter of the working environment.

In other words, the device of the invention allows the remote acquisition of the radiofrequency signature of an RFID transponder, preferably of the passive type and also of sensitive transponders. In detail, the method implemented by this device is suitable for the characterization of sensor devices integrated in passive RFID tags.

The technical problem is solved by acquiring at a distance the electromagnetic response signal relating to a transponder (transmitter - responder, or more simply "tag") for example of the passive RF type, preferably with sensor on board.

According to a particular aspect, the object of the present invention is to identify the electrical state of a transponder starting from the spectrum of the signal associated with the magnetic field linked to it when in proximity to a suitable reader.

Advantageously, if we consider a transponder whose electrical state is variable according to a chemical / physical parameter of the environment in which it is located, the device of the invention allows this chemical / physical parameter to be measured remotely and indirectly by means of the characterization of the electromagnetic state of the transponder.

To do this, it is known (in the sense that it can be calculated and / or measured) the electrical state of the transponder to be taken as a reference (once the analytical model of the tag has been suitably fixed) which corresponds to a known value of the chemical / physical parameter neN installation environment.

In particular, knowing a spectrum of the electromagnetic signal reflected by the transponder in a reference condition, its variation is considered as a function of the parameters of the environment in which the transponder is located. The quantity of which the variation is considered is preferably the resonance frequency, which can be extrapolated from the spectrum of the signal according to known calculations.

This information is independent of the logical content of the memory of the chip integrated on the tag and ultimately of its logical identifier (in the case of RFID defined as “UUID”). Therefore, advantageously, it is also possible to operate on chip-less or damaged RFID transponders.

If there is a sensor in the RF part of the transponder circuit, the system allows the user to detect changes in the electrical response of the sensor itself.

Advantageously, the invention allows to avoid the use of the traditional instrumentation necessary for the design and verification of RFID tags, reducing costs and dimensions associated with it, preferably configuring as a portable system.

According to a further advantageous aspect of the invention, the quantity detected by the sensor possibly on board the tag can be of any nature, provided that a variation of the measurand is transduced into a variation of electrical impedance. Given the area in which the invention fits, chemical sensors and in particular gas sensors are of particular importance.

Advantageously, the invention can be used in contexts such as a contaminated, hostile or simply inaccessible environment, the need to identify the source of the sensory data, etc. in order to allow the remote acquisition of the transduced values without resorting to measuring instruments which, given the quantities involved, have already been said to be sophisticated, delicate, expensive and energy-intensive.

To obtain this result, a "custom" reader was designed which, unlike commercial readers, is not able to read the logical content of the memory of a transponder, but which is rather designed to construct a representation of the status of the sensor based on the interrogation, frequency by frequency, of the intensity spectrum of the signal reflected by the transponder.

In particular, the invention makes it possible to detect the variations in the admittance of a transponder - preferably passive - which may be due to the variation in the admittance of a sensor electrically connected to the RF part of the transponder circuit, the state of wear of the tag or of the chip or the very nature of the chip, interconnections or substrate adopted in the synthesis of the tag.

Advantageously, this operation is carried out without requiring the use of a direct connection (wired) between the reader and the tag circuit, nor of a network analyzer (VNA), a spectrum analyzer, an impedance analyzer, or a oscilloscope, as instead required by the solutions present in the known art.

According to particularly advantageous embodiments, the invention is preferably of the portable type and is of low weight and compact size.

According to a further aspect, the invention has low construction costs and energy consumption.

Furthermore, the device of the invention can be equipped with connection means, for example USB, with a computer or communication networks in general.

In particular, as will be better appreciated in the detailed description below, it is possible to vary the width of the frequency range to be investigated, the frequency resolution with which the spectrum of variations is acquired and the accuracy of the measurement of the response amplitude. of the tag.

According to preferred embodiments of the invention, the acquisition times of the transponder response signal to the magnetic field transmitted by the reader device are very low (in the order of seconds).

Furthermore, advantageously, the invention turns out to be an extremely economical system (achievable by widely used commercial circuitry), accurate as regards the generation of the interrogation frequency (probing), not linked to the need to have mains power supply or instrumentation. dedicated measurement.

Furthermore, embodiments of tags compatible with the device of the invention can be derived in a simple way from commercial RFID HF tags (for example standard MIFARE) by modifying the circuit with the insertion of a preferably capacitive sensor in parallel to the antenna.

Therefore, the logical information can be retrieved using a standard reader (if the characteristics of the passband and sensitivity of the tag downstream of the sensor admittance variation are still compatible with conventional RFID systems) and the costs of the transponders are very low because there is no need to use dedicated chips.

According to preferred embodiments of the invention, the proposed system has a flexible configuration, for example the holder for the tag containing the antennas can be detached from the main body of the device, facing surfaces of environments to be monitored or integrated into objects in common use, architectural elements or in other products.

In a more detailed perspective, a preferred method of the approach followed is to modulate the admittance of the transponder through the admittance variation of a sensor. This strategy can also be verified in the laboratory through impedance measuring instruments, which are relatively simple to find and not very complex.

In particular, the design and verification of the RFID tags included in the system of the invention can be supported in the laboratory by measuring the admittance (or impedance) spectrum of the system by using a vector network analyzer (VNA) connected to a standard wire-loop antenna.

In fact, when a sensor capable of changing its impedance according to the type and concentration of the analyte is connected in the circuit of an RFID transponder, the variation in the complex impedance of the sensor is reflected in the admittance spectrum of the tag.

Therefore, through a VNA connected to an antenna with standardized characteristics, the variations in the sensor response can be measured at a distance.

According to a further aspect, the device of the invention is suitable for the characterization of sensors for gases and vapors, and can play an important role in the development of new sensitive materials, sensor devices, pattern-recognition methods and in general sensory systems capable of monitor complex mixtures of gases and vapors.

Other advantages, characteristics and methods of use of the present invention will become evident from the following detailed description of some embodiments, presented by way of non-limiting example.

Brief description of the figures

Reference will be made to the attached figures, in which:

Figure 1 shows a schematic view of a first preferred embodiment of a system and a device according to the present invention;

Figure 2 shows a schematic view of a second preferred embodiment of a device and a system according to the present invention;

Figure 3 shows an exemplary graph of calibration data of a device according to the present invention;

Figure 4 shows a schematic plan view of a preferred embodiment of a transponder according to the present invention;

Figure 5 shows a schematic cross-sectional view of a capacitor with an interdigitated structure;

- Figure 6 shows an example of an interdigitated structure capacitor, taken from “Progress In Electromagnetics Research B, Vol. 7, 2008”;

Figure 6A shows a schematic view of a preferred embodiment of the contact geometry of an interdigitated structure capacitor according to the present invention;

Figure 7 shows a perspective view of a preferred embodiment of a support included in a device according to the present invention;

Figure 8 shows sectional views of the support shown in Figure 6;

- Figure 9 shows two graphs that respectively illustrate the trend of a resonant frequency of the device in the absence of a transponder and the trend of the resonant frequency of the device in the presence of a transponder linked to its magnetic field;

Figures 10A-10D show graphs of the calibration curves of the device according to the present invention;

- Figure 11 shows a preferred embodiment of a software architecture of a device management program according to the present invention;

- Figure 12 shows a preferred mode of displaying the graphs relating to the trend of parameters associated with the electrical signal of the magnetic field reflected by the transponder;

Figure 13 shows a preferred embodiment of an adapter for a test chamber to be applied to a device according to the present invention;

Figure 14 shows a preferred embodiment of a test chamber for a device according to the present invention;

Figure 15 shows a front view and two side views of the test chamber of Figure 11;

- Figures 16A and 16B respectively show a graph showing the response curves of the transponder as the humidity of the working environment varies;

Figure 17 shows spectra of the envelope of the response signal of the transponder measured through the prototype of the invention;

Figures 18A and 18B respectively show a graph of the real part (R) and of the imaginary part (X) of the admittance spectrum of the response signal of the transponder;

- Figure 19 shows a graph of the resonance frequencies calculated by means of a preferred embodiment of the system according to the invention compared with the resonance frequencies calculated from measurements made with a vector network analyzer; the starting data are those extracted from the graphs of Figs. 17, 18A and 18B; And

Figure 20 shows an exemplary flow diagram of a preferred embodiment of some steps of the method according to the present invention.

The aforementioned figures are intended solely for illustrative and non-limiting purposes.

Detailed description of preferred embodiments

Referring initially to Figure 1, a first preferred embodiment of a system according to the present invention for the remote measurement of a chemical / physical parameter of an environment, based on the characterization of the electromagnetic state of a transponder located in that environment, is denoted altogether with 100.

The system 100 first of all comprises a measuring device or more simply reader 10 and a transponder 1, preferably a passive RFID tag, which is referred to hereinafter also more simply as a tag.

The transponder 1 is configured in such a way as to present one or more variable electrical / magnetic parameters as a function of said chemical / physical parameter detected, in particular a variable electrical parameter such as an admittance or electrical impedance. The variation of these parameters causes a corresponding variation of the electrical signal associated with the reflected magnetic field of the transponder, in particular of the resonance frequency of the intensity spectrum of the signal. In order to appreciate this variation, the values of the electromagnetic parameters of the transponder are known with respect to a reference condition, in which the value of the chemical-physical parameter in question is known.

Transponder 1 is preferably equipped with a sensor dedicated to measuring a chemical / physical parameter of the environment in which it is installed.

For example, the sensor can be suitable for measuring the concentration of a gas or the concentration of humidity in the installation environment of tag 1. As anticipated, the sensor is structured in such a way as to vary one or more of its electromagnetic parameters depending on the characteristics of the environment in which it is immersed. For example, you can use a tag equipped with a capacitive sensor, whose electrical capacity varies according to the humidity of the installation environment.

To a change in capacitance, or more generally in an electromagnetic quantity, of the sensor, there corresponds a commensurate change in capacitance, or more generally in an electrical parameter in the circuit relating to the tag 1 considered as a whole.

The electromagnetic specifications of the sensor, as well as those of the tag, are known a priori with respect to the reference environmental conditions, according to what has already been described.

It is particularly advantageous to use a sensor of the capacitive type, in particular chemio-capacitive whose electrical / magnetic parameter which varies according to the chemical / physical parameter detected is the electrical capacitance.

Preferably, sensors of the capacitive type are used which behave like an electric capacitor, in particular having an interdigitated structure.

For a sensor configured for the detection of humidity in the environment, the structure of the condenser may preferably comprise an alumina substrate, two silk-screened gold contacts and a hygroscopic polymer having a high affinity for water, preferably soluble in water, as a substance. sensitive to the parameter to be measured, for example poly (vinyl alcohol).

The reader or reader 10 is configured for the remote characterization of the electromagnetic state of transponder 1 and for the consequent indirect measurement of the chemical / physical parameter of the environment measured precisely by transponder 1.

The characterization of the electromagnetic state of the tag is carried out by the reader 10 substantially by means of the remote transmission of an electromagnetic signal to the transponder 1, the remote acquisition of the electromagnetic response signal of the same transponder and the extrapolation of the electromagnetic status of the tag 1 by means of response signal processing. To carry out the characterization of the environment in which the tag is immersed, at least with respect to the physical / chemical parameter according to which the electromagnetic parameters of the sensor on the tag are variable, a comparison of this electromagnetic response status with the status is carried out. electromagnetic of the tag - known a priori - in a reference condition in which the value of the chemical / physical parameter considered is known. Naturally, the law that expresses the variation of the electromagnetic parameter (s) of the sensor as a function of the chemical / physical parameter considered is also known.

For this purpose, the device 10 comprises a control and data processing unit 6, a generating unit 5 for an electrical signal and a receiving unit 7 for an electrical return signal, both connected to the control unit and processing 6, and of the electromagnetic coupling means 4 with the transponder 1.

In particular, the generation unit 5 is configured to generate a sinusoidal electrical signal, preferably numerically controlled, from the control and processing unit 6. Preferably, the generation unit 5 comprises a digital signal synthesizer, for example a synthesizer direct digital, for setting the power supply frequency of the electrical signal.

The electromagnetic coupling means 4 with the transponder 1 comprise a transmission antenna (probing coi I) 2, connected to the generation unit 5, configured for the diffusion of a magnetic field corresponding to the electrical signal of the generation unit 5 in correspondence of transponder 1.

Further, the means 4 comprise a receiving antenna (sensing with I) 3, connected to the receiving unit 7, configured to concatenate the magnetic field reflected by the transponder 1.

The transmitting and receiving antennas 2, 3 can each comprise a solenoid. Preferably, the transmission antenna 2 is configured for the diffusion of a magnetic field that is also suitable for powering the transponder 1, when this is of the passive type.

In particular, the transmission antenna 2, the reception antenna 3 and the transponder 1 constitute a closed loop system from an electromagnetic point of view.

The receiving antenna 3 is further configured to transmit an electrical return signal corresponding to the magnetic field reflected by the transponder 1 - function of the variable electromagnetic parameter of the transponder 1- to the receiving unit 7.

This receiving unit 7 is programmed to transmit said electrical return signal to the control and processing unit 6, which is in turn programmed to process the electrical return signal.

The control and processing unit 6 is configured to calculate a value of the chemical / physical parameter of the work environment in which tag 1 is located on the basis of the comparison between the acquired electrical return signal and a reference return electrical signal under known environmental conditions and of the relationships between said parameter and the electric return signal.

As anticipated, the magnetic field reflected by the transponder 1 and the corresponding electric return signal sent to the control and processing unit 6 are variable according to the variable electromagnetic parameter of the tag 1. In particular, the complex impedance variation of the sensor is reflects on the admittance spectrum of the transponder, so this characteristic can be measured from a distance.

The receiving unit 7, connected to the control and processing unit 6, can be further designed to perform a conditioning of the return electrical signal before transmitting it to said control and processing unit 6.

The conditioning is carried out to allow a more accurate reading of the signal, therefore to better appreciate the variations of the variable electromagnetic parameter and consequently to calculate more accurately the chemical / physical parameter of the monitored environment according to which the electromagnetic parameter is variable. In particular, the reception unit 7 comprises a demodulator 8 of amplitude of the electrical signal corresponding to the magnetic field reflected by the transponder and an A / D converter 9 of the electrical signal, adapted to convert the signal from analog to digital.

According to preferred embodiments of the invention, the receiving unit 7 comprises the demodulator 8, the converter 9 and the receiving antenna 3. In particular, between the sensing coil 3 and the demodulator 8 it is possible to introduce a tuning circuit capable of adapting the passband of the receiving unit 7 to the band characteristics of the envelope spectrum to be detected. The control and processing unit 6 is programmed to process the conditioned electrical return signal from the receiving unit 7 and to calculate the chemical / physical parameter of the environment as a function of said conditioned return electrical signal, according to the considerations illustrated in precedence. In addition, the control and processing unit 6 can also be configured to simply retransmit the data relating to the envelope to a higher-class processing system. The latter is suitable for extracting the physical parameters to be measured starting from the spectrum of the enveloped signal. In particular, the control and processing unit 6 is programmed for processing an intensity spectrum associated with the magnetic field reflected by the transponder, a function of the variable electrical / magnetic parameter. The electrical parameters that qualify and quantify the performance of the transmission channel (and ultimately of the transponder 1) can be extrapolated from the intensity spectrum (or RF signature), such as resonance frequency, bandwidth, quality factor, etc.

Examples of such processing and calculations will be illustrated below.

In addition, the control and processing unit 6 may comprise interface means 12 to allow its command (even remotely) by a user. According to a preferred embodiment of the device of the invention, the interface means 12 preferably comprise a monitor for viewing the electromagnetic spectrum associated with the magnetic field reflected by the transponder and the software that interfaces with the acquisition system, represents the graphs relating to further processing and exposes the controls necessary for the configuration of the reader.

As anticipated, an aim of the invention is to identify the electrical state of a transponder starting from the spectrum of the signal associated with the magnetic field linked to it. If a sensor is present in the RF part of the transponder circuit, as in the preferred embodiment of the invention described above, the system allows the user to detect changes in the electrical response of the sensor itself.

The acquisition of sensory data can be carried out not only by a single transponder, but in parallel by an array of sensitive transponders, replicating the architecture of the reader device 10, or serially, bringing new transponders in the vicinity of the apparatus from time to time. reader the reference tag-sensor, or multiplexing the acquisition channel and replicating the antennas interfacing with the transponder.

A more detailed prototype variant of the architecture of the system 100 of the invention will be described in detail below.

An interfacing system of the measuring device 10 synthesizes a sinusoidal signal of variable frequency and transmits it to the tag by coupling with it through the antenna or interrogation coil 2 ("probing coil"). The acquisition chain detects the envelope of the electrical signal due to the magnetic flux which is chained to the solenoid of the receiving antenna 3 ("sensing coil" - SC) placed between the antenna or transmitting coil 2 (also in the shape of a solenoid) and tag 1 equipped (or not) with the sensor.

The technique implemented for the characterization of transponder 1 is therefore based on the interception of the signal transmitted between a numerically controlled sinusoidal generator and a transponder 1. The natural time constants relating to the physical layer of the transponder and the possible presence of a sensor intended as electronic component with its own electrical impedance introduce one or more resonance peaks into the entire system 100. These peaks can be detected by acquiring the spectrum of the signal at probing coil 2.

Between the transmitting coil 2 of the reader 10 and the receiving antenna of the transponder 1, the magnetic flux is chained to an additional reading coil 3 according to a "Man-ln-The-Middle" (MITM) approach, as shown in Figure 1 and 2.

Neglecting the non-linearities (which generally trigger in tags equipped with chips), the electrical signal taken from the sensing coil 3 is characterized by a frequency equal to that of the generated signal and by an amplitude dependent on the impedance module of the transmission channel, and therefore ultimately from the electrical state of the sensor.

An intensity spectrum related to the field linked to the SC 3 can be constructed by varying the frequency of the generator that feeds the probing coil 2 (PC) and by recording the envelope of the signal detected by the SC 3. To do this, it is necessary to connect the SC with an amplitude demodulator (ASK demodulator), which in the simplest case can be realized through a single half-wave rectifier, as illustrated in detail in Figure 2.

Consider a sensitive tag including a sensor for detecting a chemical / physical parameter of the work environment in which the tag is installed, for example for measuring environmental humidity. Being able to schematize the tag as a resonant RL-C circuit with the capacitors in parallel (see again Fig. 2), as a first approximation, the resonant frequency of the tag can be estimated by Thomson's law:

fr = i (Eq. 1)

From the proposed law it is observed that it is convenient for the sensor to be of the capacitive type because, first of all, the resonant frequency does not depend on attenuations that can occur due to different distances between the transponder and the coils of the reader (SC and PC) , and secondly because said parameter can be estimated from the maximum of the envelope signal regardless (subject to instrumental sensitivity limits) from the amplitude of the aforementioned maximum. This is due to the fact that the supply frequency is imposed through the direct digital signal synthesizer (DDS), therefore the resonant frequency can be estimated with good accuracy since it is generally fixed by construction.

In order to power the transponder, the probe coil is connected to a DDS, which in a prototype of the invention is based on the Analog Devices® AD9850 chip. The DDS in question produces a “spectrally pure” sinusoidal signal, with a frequency between 1Hz and half the reference clock frequency, which in this case is 125MHz.

Therefore, the obtainable maximum frequency sinusoid is 62.5MHz. In the DDS, the theoretical output frequency is proportional to the value assumed by a “tuning word” {ΔΦ) which expresses the value of the frequency of the sinusoid to be synthesized, described by a 32bit integer with which it is possible to program the synthesizer.

The oscillator output frequency will therefore be expressed by the relationship:

fck-ΔΦ

ose (Eq. 2) 2 <3Z>

being fa is the clock frequency at DDS {fa = 125MHz), 232 is the number of values that can be assumed by the tuning word and ΔΦ is the value of the tuning word.

In this case, the term "tuning word", in the case of the AD9850 synthesizer, for example, identifies a 32bit integer (and in general an N bit integer) proportional to the factor by which the DDS clock frequency is divided in order to obtain the frequency of the synthesized signal. It is in fact known that this proportionality factor is generally valid: ΔΦΙ2 <Ν> and that 0 <ΔΦ ≤ 2 <N> -1. Since the DDS can be thought of as a digital frequency divider, it is comparable to a lookup table comprising 2 <N> locations, each of which contains a sample of a period of a sinusoidal signal. This table is scanned by addressing the next selected location once every clock pulse (therefore at regular intervals of Mfa) by increasing the address by an amount equal to ΔΦ. It follows that every time interval Mfa the phase of the sinusoidal signal increases proportionally to ΔΦ, being ΔΦ the number of addresses of which each clock pulse advances in the scan of the lookup table. Naturally, the sequence of values taken with this method from the lookup table is reconverted into an analog signal (by means of a digital-analog converter - DAC) and suitably filtered to avoid the presence of replicas.

The output spectrum will contain both the synthesized sine wave and its replicas, the first of which will have fck-fosc frequency. Also, due to the zero-orderhold filter at the output of the DDS's Digital to Analog Converter (DAC) - the DAC represents the final stage of the DDS which reconstructs the analog version of the sinusoidal signal starting from its samples extracted from the lookup table the amplitude of the generated sinusoid will not be constant over the entire spectrum, but proportional to the module of the function: sinc (f / fck) = sin (n f / f ^) / (π f / fck).

For this reason, in detecting the envelope of the signal at the SC, a normalization operation is necessary, which for simplicity can be performed via software, for example according to the data shown in Figure 3. The calibration data shown in Figure 3 are obtained from a spectrum acquisition once the DDS is connected directly to the envelope detector, in the absence of the probing and sensing coils.

In the representation of Figure 3, the amplitude of the signal detected by the demodulator connected to the SC has been digitized through a 10-bit ADC and represented as a function of the frequency of the signal forced by the DDS. Therefore, the ordinate value is expressed on a scale from 0 to 2 <10> -1 = 1023 and is proportional to the electrical voltage across the ADC by means of the reference potential of the ADC, which in this case is 1.1V. The presence of the reference is a consequence of the fact that the ADC adopted is of the SAR type.

On the basis of this normalization, and in the absence of transponders, the reader detects a peak in the envelope spectrum, Venv (f), at its natural resonance frequency mainly due to the value of the inductance of the probe coil and the exposed impedance to your front door from the envelope detector.

In the prototyping phase of the system of the invention, in order to analyze the readings obtained through the reader thus created, a test transponder was built, hereinafter referred to as a "dummy tag" to underline that it represents a fictitious model (but congruent with the electrical parameters typical) of the actual transponder.

In detail, the dummy tag is a reference transponder (preferably chipless) built for the purpose of calibrating the reader as defined in the architecture described above (Fig. 1) and at the same time studying the frequency response of capacitive sensors when connected to a antenna of a known type.

The dummy tag consists of an antenna made on a 12.5pm thick printed circuit, equipped with pads between which two leads are soldered for the connection of a chip or a reactive load. The purpose of this connector is to allow the connection of calibration devices or sensors to be tested. In particular, discrete capacitors are connected to the terminals of the dummy tag, with capacitance previously measured with laboratory instruments (impedance analyzers).

Figure 4 shows a preferred embodiment of the dummy tag architecture, while Figure 9 shows a graph of the comparison between the spontaneous resonant frequency of the reader and that in the presence of dummy tags not connected to capacitive load.

Using the dummy tag coupled with the calibrated capacitive loads, calibration curves of the frequency of the first resonance peak as a function of the load capacitor capacity have been obtained, reported as an example in Figures 10A and 10B.

On the basis of the data of figure 10A (symbols), it is possible to express the resonance frequency according to the model already described in Equation 1 in which CChip = 0F has been set (Fig. 10B). In these hypotheses, being linear the relationship between 1 / ωΓ <2> and the load capacity Csensor (with ω, = 2π · ί) - which in the graphs is called C (F) ~ from Figure 10B it can be seen that the model is in good agreement with the experimental data when assuming: Lanf = 6.17pFI, Ctuning = 8.27pF.

It should be noted that, by connecting one or more capacitors to the heads of the leads of the dummy-tag, an electrical diagram is created that circuitally reproduces the circuit of the tag in Figure 2. whose resonant frequency is calculated by means of Eq. 1. It remains to be noted that although a tuning capability as schematized in Fig. 2 and reported by Eq. Is not physically present on the dummytag. 1, there is always a capacitive factor (which we can still call tuning capacity) due to the parasitic couplings between the antenna tracks and the substrate. The value extracted for Lant from the LR-C model can be compared with that measured by an impedance analyzer at a frequency of 10MHz (in this case, the limits of the characterization system do not allow to go further): Lant (measured) = 7.27 μΗ, Rant (measured) <=> 3.3 Ω, validating the approach followed.

After checking the system with commercial capacitors, it was tested. In detail, in order to validate the reader, the first experimental tests were carried out by measuring the "dummy tag" to which a sensor hosted by a separate (alumina) substrate was connected through the two-lead socket.

In particular, a capacitive sensor was chosen and RF signature variations were recorded in the presence of different moisture concentrations.

The choice of a capacitive sensor is also attractive because it allows to reduce the active power and therefore to design energy-efficient transponders, to make the detection less dependent on the distance between the sensor and the reader and more accurate since it is based on the evaluation of the displacement of the resonant frequency (note that the carrier frequency is established by the DDS with a high accuracy - in the demonstrator: 1 Hz).

Furthermore, as already mentioned, the chemical-capacitive sensors are proving effective in sensing environmental humidity, but also in solvents, volatile organic compounds (VOC), toxic chemical materials, products for war use, polluting explosives (carbon dioxide and ammonia ), echo..

An analysis and description of a preferred embodiment of the sensor architecture to be adopted follows.

According to a preferred embodiment of the present invention, the sensor on board the tag comprises a capacitor, whose electrical capacity value varies according to the concentration of the analyte (VOC, gas, etc.) to which it is exposed.

As is known, the electric capacity of a capacitor is proportional to the dielectric permittivity of the insulating material, in particular ε = ε0 <'> εη being ε0 the dielectric constant of the vacuum and εΓ the relative dielectric constant of the insulating material.

Therefore, the variation in the capacitance of the capacitor due to exposure to a gas / vapor changes the relative dielectric constant of the material as a function of the percentage of analyte that penetrates the insulating material.

At the frequencies of interest, the capacitance values to be introduced for the tuning of the tag network are in the order of pF (picoFarad).

These values are particularly easy to obtain even without necessarily manufacturing capacitors with flat and parallel faces, but preferably resorting to an interdigitated structure, the cross section of which is shown by way of example in Figure 5.

Due to these and other reasons (which will be made explicit in the following), an IDC (Inter-Digital Capacitor) structure is preferable which, unlike a flat and parallel face capacitor, has coplanar plates.

Advantageously, this type of capacitor can be realized in only two process steps (armature deposition on the substrate and insulating deposition).

In addition, the capacitors with interdigitated structure have the dielectric with a face completely exposed to the analyte (since it is not obscured by the armature itself), and on the same dielectric it is possible to avoid curing processes, which are instead recommended in overlapping armor structures. The type of geometry used is suitable for obtaining capacity values in the order of pF as required for the specific application created.

In particular, the latter solution is considered preferable since the interdigitated capacitors (Inter Digitated Capacitors - IDC) have:

- high surface exposed to the analyte: it is known that the sensitivity and the lower detection limit of a transducer of this type depend on the surface that participates in the interaction with the environment, and that therefore the surface-volume ratio is a determining factor;

- reduced construction complexity: this type of architecture can be manufactured by simultaneously depositing the two capacitor plates on the substrate (if proceeding by screen printing or vapor phase deposition or other additive technique) or by patterning the layout of the plates starting from a conductive layer uniform by subtractive technique (photolithography, etc.); And

- greater immunity to defects, since the dielectric is applied after making the armatures, therefore it is easier to obtain capacitors without pinhole, easier to verify and more reliable.

The structure of IDC ("Inter-Digitated Capacitar" or "Inter-Digitized Capacitor") used in the prototype in question is made up of an alumina substrate with two silk-screened gold contacts, having the geometry shown in Figure 6 and 6A, which are reported in Table 1 of the preferred geometric parameters.

Table 1

Finger width (Au) 400 pm

Distance between fingers (Gap) 300 pm

Length of the area facing finger 4200 pm

Finger length 5600 pm

Gold thickness 80 pm

Runway width 1000 pm

Number of fingers 10

As for the electrical capacity, in the hypothesis of a homogeneous and isotropic dielectric film, this can be calculated by adding the contribution of the "cells" that make up the interdigitated, according to known calculations.

That the electrical capacity of this device is compatible with the hypothesized application can be deduced from the models developed for the IDCs. In detail, the electrical capacity of the device of Fig.6A can be expressed by the relations:

CT0TALE = CCeua (N - 1) L (Eq. 3) K (jl- (a / b) <2> ^

Cell C ^ r <Z> k) (Eq. 4)

K (a / b)

This relationship expresses the total CTOTAL capacity of an interdigitated capacitor having N fingers or fingers of length L arranged according to the geometry of Fig. 6a as a function of the capacity of the unit cell Cce // adell IDC.

The unit cell of the IDC is an architectural element repeated with a uniform step of spatial periodicity b that contains two fingers of thickness t that are distant from each other by a length a. In Equation 4, ε0 is the dielectric constant of the vacuum, εΓ the relative dielectric constant of the substrate, the relative dielectric constant of the dielectric and K the complete elliptic integral of the first kind.

It follows that the capacitance of the sensor varies proportionally to the variation of the average relative dielectric constant of the sensitive dielectric. In the Maxwell Gameti approximation, the average dielectric constant depends on the volumetric fraction of the analyte absorbed by the sensitive dielectric layer. Therefore, it is possible to make a preventive estimate of the variation in the frequency of the resonance peak of a tag as a function of the volumetric concentration of the analyte or an a posteriori analysis of the data relating to the resonance frequency.

On the basis of the models for the sensor capacitance and for the average dielectric constant (Maxwell Gameti) it is possible to estimate what the response of the dummy tag will be (see graphs of Fig.10C and 10D) as a function of the volumetric concentration of the analyte in the sensitive film .

The graphs of Figures 10C and 10 show a simulation of the response of the dummy tag to the variation of the volumetric fraction of analyte in the sensitive film. In particular, Figure 10C shows the relationship between the resonant frequency of the transponder and the equivalent dielectric constant of the sensitive film (resulting from the variation of the dielectric constant of the film in combination with the dielectric constant of the analyte), and Figure 10D shows the relationship between the resonance frequency of the transponder and the volumetric fraction of the analyte in the sensitive film predicted through the Maxwell Garnett relationship.

The simulations considered were obtained assuming the alumina substrate (εΓ (Αΐ2θ3) = 9.19), the inductance L of the dummy tag equal to the measured value L = 6.17pH, the total capacity of the dummy tag equal to Co = 8.27pF, the dielectric constant of the analyte equal to that of water (εΓ (Η2ο, 25 ° c; = 78), the dielectric constant of the sensitive film equal to that of the PVA and the architecture of the contacts equal to that shown in Fig. 6A.

This approximation, albeit with all the limits imposed by the simplifications performed, shows that it is possible to obtain variations in resonance frequency even of 1MHz in correspondence with the operating conditions described and that the maximum sensitivity is obtained for small values of analyte volume fraction.

A preferred embodiment of the sensor architecture used in the prototype of the system according to the present invention will now be described in greater detail.

A capacitive sensor capable of detecting air humidity was produced by drop-casting a solution of a hygroscopic polymer deposited on a structure of interdigitated gold contacts. The polymer chosen as sensitive material is poly (vinyl alcohol) (PVA), a low cost material, easily workable from solution. PVA is characterized by a high affinity with water thanks to the high number of hydroxyl groups present in its structure, which make it able to absorb water molecules and form hydrogen bonds with it. This produces a change in the dielectric constant of the sensitive films, even taking into account the difference between the two relative dielectric constants (2.5 for PVA and 80 for water when measured at 20 ° C and at 1kHz). Several studies have highlighted the possibility of using this polymer in sensor applications for the detection of humidity in a wide range of frequencies (0.2-20 GHz).

The sensor was made starting from an aqueous solution of PVA prepared by hot melting the PVA (weighted average molecular mass Mw = 67000g / mol) in deionized water in a concentration of 100mg / mL. The molecular mass and the concentration of the polymer have been defined in order to make the solution also suitable for potential printing processes using ink-jet printing technology which require specific chemical-physical properties of the inks to be dispensed and which could be of interest for a possible industrialization of the sensor prototype. The choice of this material is indicated for detecting variations in humidity, since it is known that water is a solvent for PVA and that, due to the difference between the two relative dielectric constants, an increase in the sensor capacity is expected as the RH% value.

A preferred embodiment of the physical architecture of the measurement device (reader) will now be described in greater detail.

The electrical part of the reader consists of the microcontroller board (which integrates the ADC, the voltage reference for the converter and the USB interface) connected to the DDS board and finally by a printed circuit containing the amplitude demodulator, as schematized in Figure 2.

Figure 7 shows in detail the seat or support 14 for the reader coils.

The sensing and probing coils are wound on the support 14, designed to minimize the distance between the interface of the reader and the transponder.

In particular, the transponder (in the prototype assumed in the form of a card with ISO / IEC 7810 ID-1 geometry) is placed on the support 14 at the location of the transponder 15, which in this case has the preferred dimensions 85.60 mm x 53, 98 mm but could of course have arbitrary dimensions. Aligned with the seat of the transponder 15, the PC and the SC are present in the relative seats 16, 17, wound on a core of plastic material of which the support 14 is made.

The insulated conductors (“strands”) that make up the coils are conducted in the external area behind the support through the grooves 18. The seats of the coils are better visible in the section view of the support shown in Figure 8.

Again with reference to Figure 8, the dashed rectangular part included in the seat of the transponder 15 is the core of the windings PC and SC.

We will now describe in greater detail a preferred embodiment of the software architecture that governs the control and processing unit of the reader device, referred to below for simplicity as a microcontroller.

The firmware of the reader microcontroller manages the acquisition operations from the ADC and the communication protocol to the computer.

Leaving aside the accessory functions, it operates by essentially repeating the following operations in a cycle:

- wait for a command from the serial interface;

- if an acquisition command arrives (single, multiple, in log), set the oscillator (DDS) to the FSTART frequency;

- send on the serial interface the line: "> start":

1. read the signal envelope value on the PC from the ADC;

2. send a line on the serial channel containing the value of the set frequency (long) followed by the "tab" character and the value read by the ADC (10bit integer);

3. increase the frequency «f» of the DDS by the FSTEP value;

4. if f <= FSTOP go back to step 1;

- send on the serial line the line: “> stop”.

Through appropriate configuration commands, it is possible to set the starting frequency (lower limit) for the acquisition of the spectrum (FSTART), the upper limit in frequency of the scan (FSTOP), the frequency acquisition step (FSTEP), the time of wait between one acquisition and the next and the number of rereadings of the sample from the ADC (the rereadings are averaged via software to provide a more accurate value for the Venv envelope signal).

Along with the reader, an appropriate computer software interface has been implemented in order to acquire the data through the serial interface from the reader and vary the measurement limits (number of readings, frequency resolution, measurement interval, etc.).

Figure 11 shows a preferred example architecture of the reader management program.

The software, written specifically in Java ™ language, is a desktop application. It opens a computer serial port for reading (typically emulated by a USB port) and waits for data to arrive from the microcontroller board. Each arrival of one or more bytes generates an event that causes the related data to be written to a buffer. When the carriage return character (“\ n”) is encountered in the data stream, a line is ready. In this case, the buffer is passed to a parser and then emptied. The parser extracts the data, processes them by calculating Venv based on the calibration data, appropriately formats the line to persist in a log file and notifies a software component called logger, which will then write a local ASCII file. Each time valid data arrives (ie "well formatted"), the measurement graphs are updated as well as the relative scales, providing the user with a real-time view of what is happening to the sensor. By way of example, a screenshot of the acquisition software is shown in Figure 12.

In the current version, the program allows you to acquire and compare tag signatures both in a modulus / frequency diagram and in a "colormap" (right screen in Figure 12) which is more useful for comparing data from repeated acquisitions in the time. The system can work by performing one-shot acquisitions (single - using the "Get Data" button), repeated (10 times - "Get Sequence" button) or continuous ("Log" button).

From the user interface you can preferably modify: the step of the frequency scan ("fstep" - in Hz), the acquisition delay between one sample and another (delay - in ms), the number of re-readings of the single bin ( rereads), it is also possible to limit the acquisition interval (“set limits”), allowing to reduce acquisition times.

Basically, a transponder data acquisition system with on-board sensor based on the variation of the resonance frequency was created. The system was calibrated using an artifact ("dummy tag") also useful for the remote characterization of IDC sensors. Finally, the system was physically adapted to the characteristics of a climatic test chamber and verified with a polymeric IDC sensor by comparing the input-output curve with the one extracted using standard laboratory instrumentation for the characterization of RFID tags.

For the sake of completeness, an experimentation protocol of the prototype of the system of the invention will be described below.

The reader was experimented by creating an overpressure climatic test chamber. The test chamber is made using the upper surface of the reader, enclosing the transponder within an overpressure environment in which the gas streams containing the analyte are adducted and extracted. This condition is implemented solely for system testing and validation purposes.

In particular, the climatic test chamber has as walls the holder for the reader tags, a plexiglass cap and a perforated adapter. The whole is held together by four screws and the interstitial areas are sealed. The adapter, which fits onto the reader at the winding support shown in Figure 7, is depicted in Figure 8. Figure 8 shows the test chamber compartment and the threaded holes used to fix the chamber lid.

In this way, the environment that contains the dummy tag is directly interfaced with a humid air generator with a controlled humidity percentage. The discussion does not lose generality if a carrier gas is introduced into the test chamber in which an analyte other than water is dissolved.

Figures 13 and 14 show the equipment adopted to test the prototype of the invention system in simulated climatic conditions of the acquisition system interfaced with dummy tags.

The test chamber 20 is mounted on the reader. The transparent cover 18 is fixed to the adapter by means of the fixing screws 26 inserted in the holes 19. Inside the test chamber 20 there is a USB connector 27 and the atmosphere is conditioned by continuously supplying through the inlet pipe 21 carrier gas to which the analyte is mixed.

The pressure inside the chamber 20 is higher than the atmospheric one, therefore the atmosphere inside it can be said to be uniquely determined by the composition of the gas introduced. The analyte, in the vapor phase, modifies the electrical impedance of the capacitive IDC sensor 22 connected to the antenna of the dummy tag 23 by means of two leads or electrical connectors 24. The excess gas is removed from the chamber by means of the exhaust pipe 25 which comes out of the transparent cover.

The geometry of the test chamber 20 is better visible from the constructive schematic representation of Figure 15.

In the Proof of Concepì (POC) performed and described here, the test chamber was connected to a humid air generator in order to validate the system through a humidity sensor.

Under test conditions, the humid air generator operated in the following conditions: humidity supplied by the bubbler, Tgas = 25 ° C; gas flow in the chamber: 497cc / min; carrier gas: nitrogen.

As a first experiment, the responses of the RF signature of the envelope to the dry air / humid air and humid air / dry air transitions acquired by the reader were analyzed, shown respectively in the graphs of Figures 16A and 16B, with reference to a PVA sensor. These graphs report the transient evolution of the spectrum portion of the signal envelope starting from the state of maximum humidity of the carrier gas to that of the "dry" regime.

The acquisition was achieved by first scanning from 1MHz to 30MHz in 5KHz steps, then restricting the analysis range to a convenient around the resonant peak in order to reduce acquisition times. The scanning step has been reduced to 1KHz to obtain a higher frequency resolution.

It can be observed that the increase in relative humidity from 6% (dry condition) to 62% (maximum humidity possible in these measurement conditions) corresponds to a reversible variation of the resonance frequency of about 120KHz, which according to the model developed for the dummy-tag being calibrated is equivalent to a shift in capacitance from 7.1pF to 6.9pF.

It is therefore essential to reduce the intrinsic capacity of the transponder in order to access the area of the volumetric fraction / resonance frequency response with a higher slope.

The response of the system was checked on a second sensor at different relative humidity values after the steady state was reached at the set temperature of 30 ° C.

From the envelope spectra shown in Figure 17, it is observed that the TAG + reader system exhibits two resonance peaks, a primary peak at 16.5MHz and a secondary peak at 25.85MHz.

The frequency of the primary peak decreases as the moisture concentration increases as expected.

In particular, Figure 17 shows a graph of the response of the PVA2 sensor to the variation of the relative humidity level.

To validate the system, as a term of comparison, the impedance spectrum of the dummy-tag was acquired through a Keysight 5061 B VNA coupled to the dummy tag through a standard wire-loop antenna, obtaining the variations shown in the graphs of Figures 18A and 18B, being Z (jai) = R (ai) + jX (ai).

In particular, Figures 18A and 18B show the admittance spectra of the dummy-tag acquired by means of the VNA in coupling to a standard wire-loop antenna.

Figure 19 shows a comparison between the resonant frequency of the dummytag + wire-loop + cables + VNA (·) system with the dummytag + reader (■) system.

By graphing the trend of the resonant frequency acquired at the different RH% and comparing the values obtained by the reader with those measured with the VNA, concordant variations are obtained for the response curves, as shown in Figure 19.

The difference in the absolute value of the resonance peak frequency detected between the two devices shows that the reader introduces a reactive component in the measure that lowers the resonance frequency acquired with this method. This is due to the fact that the pick-up antenna (PC) has a greater inductive component than the wire-loop and to the fact that the demodulator loads this antenna with a non-negligible capacity. Nevertheless, with the same sensor, the system is able to appreciate the variations of the RH in the same range as the laboratory instrumentation.

Furthermore, Figure 20 shows a flow diagram illustrating the different acquisition and processing phases of the signal acquired in the reader / tag interaction.

Table 2 below provides an explanation of the symbols used in Figure 20 and in this discussion.

Table 2.

DAC Digital to Analog Converter - digital-to-analog converter.

DDS Direct Digital Synthesizer - direct synthesizer digital signal synthesizer.

Probing Coil Power Antenna. It supplies electrical power to the transponder by means of an inductive coupling in the PC field

Neighbor.

Transponder Tag, transmitter-responder, the circuit that is interrogated by the reader.

fdds Frequency of the sine wave generated by the DDS. It is set by the microcontroller communicating it to the DDS in digital format.

fstart The spectral range to be analyzed is (fstart, fstop), therefore fstart is the lower extreme.

fstop See fstart.

Sensing Coil Sensing coil. It intercepts the magnetic field and its variations in the path to the transponder.

f.e.m. Induced ElectroMotive Force.

Venv Amplitude of the electrical signal taken from the probing coil.

Envelope signals.

ASK Amplitude Shift Keying, amplitude modulation.

ADC Analog to Digital Converter, analog-digital converter.

PC Personal Computer, electronic computer.

USB Universal Serial Bus.

The preferred flow of acquisition operations operated by the reader is shown in the following sequence:

1. set the DDS frequency to the fstart value (ie: fMs <- fstarì)]

2. transmit the synthesized sinusoid to the transponder by means of the probing coil;

3. take the signal associated with the linked magnetic field both to the transmitting antenna ("probing coil") and to the transponder by a third coil ("sensing coil") placed between the first two;

4. demodulate the value of the f.e.m. at the ends of the probing coil by means of an amplitude demodulator in order to extract the envelope value

(Venv)]

5. digitize the output voltage Venv to the ASK demodulator through an ADC and transfer it to the microcontroller;

6. send the pair (fdds, Venv) from the microcontroller to the PC;

7. increase to the frequency of the DDS by the step fstep (ie: fdds <- fdds + fstep) <'>, and

8. if fdds <fstop, repeat the operations described starting from step 2, otherwise finish the operations.

As regards the manufacture of RFID transponders, this lends itself to an on-line verification of the conformity of the tags produced by means of a low cost / low complexity / low encumbrance / portable system. The verification of the individual pieces lasts in the order of seconds and can be entirely managed by an automatic system since the reader based on MCU can be programmed and managed remotely.

The sectors of application of the device and of the system proposed according to the present invention are many, such as:

- detection of toxic / dangerous / explosive contaminants;

- logistics;

- stateful tracking of packaged goods;

- anti-counterfeiting, anti-contamination, anti-tampering;

- food safety;

- vacuum-packed or packaged foods with controlled atmosphere packaging;

- controls on the cold chain;

- package integrity check; And

- monitoring of biological materials in a conditioned environment, culture substrates, incubators, other confined areas such as areas with high biological risk, "sterile" areas, and areas with conditioned atmosphere (oxygen / hyperbaric chambers, echo).

The present invention has been described up to now with reference to preferred embodiments. It is to be understood that there may be other embodiments that refer to the same inventive core, as defined by the scope of the claims set out below.

Claims (21)

CLAIMS 1. Measuring device (10) for the remote detection of a chemical / physical parameter of a work environment by characterizing the electromagnetic state of a transponder (1) located in said work environment, which transponder (1) is configured in such a way as to present a variable electrical / magnetic parameter as a function of the chemical / physical parameter according to a known law with respect to a reference condition, which measuring device (10) comprises: - a data control and processing unit (6); - a generation unit (5) of an electrical signal connected to said control and processing unit (6); - a receiving unit (7) of an electrical return signal, connected to said control and processing unit (6); - electromagnetic coupling means (4) with the transponder (1), in turn comprising: <■> a transmission antenna (2), connected to said generation unit (5) and configured for the production of a magnetic field corresponding to said electrical signal at the transponder (1); And <■> a receiving antenna (3), configured to link up with a magnetic field reflected by the transponder (1) and connected to said receiving unit (7) in such a way as to provide the latter with a corresponding return electrical signal to said reflected magnetic field, which electrical return signal is a function of the variable electrical / magnetic parameter of the transponder (1), wherein said receiving unit (7) is programmed to transmit said electrical return signal to said control and processing unit (6), and in which said control and processing unit (6) is programmed to process said electrical return signal and calculate a value of said chemical / physical parameter of the working environment. Measurement device (10) according to claim 1, wherein said transmitting and receiving antennas (2, 3) each comprise a solenoid. Measuring device (10) according to claim 1 or 2, wherein said transmission antenna (2) is configured for the production of a magnetic field suitable for powering the transponder (1). Measuring device (10) according to one of the preceding claims, wherein said generating unit (5) is configured to generate a sinusoidal electrical signal. Measurement device according to one of the preceding claims, wherein said generating unit (5) comprises a digital signal synthesizer for setting a frequency of said electrical signal. Measurement device (10) according to one of the preceding claims, wherein said receiving unit (7) is programmed to perform a conditioning of said electric return signal, preferably comprising an amplitude demodulator (8) of said electric signal return. Measurement device (10) according to one of the preceding claims, wherein said receiving unit (7) comprises an A / D converter (9) of said electric return signal. 8. Measurement device (10) according to one of the preceding claims, in which said control and processing unit (6) is programmed for processing an intensity spectrum associated with the magnetic field reflected by the transponder (1). Measurement device (10) according to one of the preceding claims, wherein said control and processing unit (6) comprises interface means (12) for control by a user, preferably comprising a monitor for displaying said intensity spectrum. Measurement device (10) according to one of the preceding claims, wherein said control and processing unit (6) is programmed for: <■> calculating the resonant frequency of said electric return signal; <■> comparing said resonant frequency with a known resonant frequency characteristic of the transponder (1) in known environmental conditions and calculating any difference; And <■> calculate the value of said chemical / physical parameter in the work environment as a function of any difference. 11. Measurement system (100) for the remote detection of a chemical / physical parameter of a work environment, comprising: - a transponder (1) configured to be localized in the work environment, which transponder (1) has at least one electrical / magnetic parameter that varies according to said chemical / physical parameter with respect to a reference condition; And - a measuring device (10) according to one of claims 1 to 10. Measurement system (100) according to claim 11, wherein said transponder (1) is a passive transponder. Measurement system (100) according to claim 11 or 12, wherein said transponder (1) comprises a sensor for detecting said chemical / physical parameter. 14. Measurement system (100) according to claim 13, in which said sensor is suitable for measuring the concentration of a gas or the concentration of humidity in the working environment. Measurement system (100) according to claim 13 or 14, wherein said sensor is of the capacitive type, in particular chemical-capacitive type, and said at least one electrical / magnetic parameter which varies according to said chemical / physical parameter detected is the capacity of said sensor. System (100) according to one of claims 13 to 15, wherein said sensor comprises a capacitor with an interdigitated structure. System (100) according to claim 16, wherein said interdigitated structure of the capacitor comprises an alumina substrate, two silk-screened gold contacts and a hygroscopic polymer having a high affinity for water, the latter preferably poly (vinyl alcohol) . Measurement system (100) according to one of claims 11 to 17, wherein said transmission antenna (2), said receiving antenna (3) and said transponder (1) constitute a closed-loop electromagnetic system. 19. Method for the remote measurement of a chemical / physical parameter of a work environment, which method includes the steps of: - providing a transponder (1) having at least one electrical / magnetic parameter which varies in a known manner as a function of said chemical / physical parameter; - place said transponder (1) in the work environment; - transmitting a magnetic field to said transponder (1); - receiving the magnetic field reflected by said transponder (1); - processing the return electrical signal associated with said reflex magnetic field; - calculating the value of said variable electric / magnetic parameter associated with said electric return signal; - comparing the value of said variable electrical / magnetic parameter with a known value of the variable electrical / magnetic parameter characteristic of said transponder (1) in known environmental conditions with respect to said chemical / physical parameter, and calculating any variation thereof; and - calculate the value of said chemical / physical parameter in the work environment as a function of any variation of said variable electrical / magnetic parameter with respect to the aforementioned known value. Method according to claim 19, wherein said transponder (1) is a passive transponder, preferably comprising a sensor for detecting said chemical / physical parameter. 21. Method according to claim 19 or 20, wherein said variable electrical / magnetic parameter is an admittance, an electrical impedance, or a capacitance.